(A) The passage states that the infection can be spread by coughing. The flu virus, therefore, can reach the other passengers in the “closely-packed environment” before it enters any filters that might kill the virus.

(B) CORRECT. Vaccines provide significant protection against developing the virus (not 100% protection, but you are asked to “minimize” the impact of air travel, not eliminate it entirely). If all passengers are vaccinated against the virus, many of those who otherwise would have developed the disease will not, and, therefore, won’t spread it to others.

(C) Anyone can contract the virus and subsequently spread it; the mentioned populations are mere “especially vulnerable” to it. Infected people traveling to another place can infect children, senior citizens, and others who have stayed in their home regions.

(D) The passage states that the infection can be spread by coughing; while it may be true that the virus can also spread via hand contact, this information is not stated in the passage.

(E) The passage states that people who develop symptoms before travel begins likely would not make the trip; weeding out those with observable symptoms, then, won’t “minimize” the role of air travel because there aren’t that many people in this category. The larger danger is those who may be infected but have not yet developed symptoms.